Stationary vanes for turbines and method for making the same

ABSTRACT

The stator vane of the present invention is provided with a leading edge which is cut into a different depth in dependence on a span-wise position so that a blade inlet angle may vary along a span-wise direction according to a prescribed pattern. By thus optimizing the depth of the cut along the leading edge of the stator vane, the leading edge blade inlet angle can be optimized along the entire length of the stator vane even if the stator vane consists of a two-dimensional aerofoil, and the vane is provided with a substantially conformal cross section in parts which are not affected by the cut in the leading edge. Thereby, the efficiency of the turbine can be optimized while minimizing the cost.

TECHNICAL FIELD

[0001] The present invention relates to stationary vanes suitable foruse in axial gas turbines and steam turbines, and a method for makingsuch stationary vanes. In particular, the present invention relates tostationary vanes that provide a high efficiency, and can be manufacturedboth easily and at low cost, and a method for making such stationaryvanes.

BACKGROUND OF THE INVENTION

[0002] Conventionally, various aerofoils have been proposed for thestationary vanes of gas turbines and steam turbines to optimizeefficiency. For instance, Japanese patent laid open (kokai) publicationNo. 10-196303 discloses a proposal in which the aerofoil is curved alongthe span-wise direction either to the back or belly of the aerofoil soas to minimize the loss due to the generation of secondary flows. It isalso known to slightly twist the aerofoil around a span axis to therebyvary the blade inlet angle of the aerofoil along the span-wisedirection. Such aerofoils are called as three-dimensional aerofoils, andare effective in improving the efficiency of the turbine. However, asthey have to be made either by casting or by computer-controlledmachining, the manufacturing process is both complex and expensive.

BRIEF SUMMARY OF THE INVENTION

[0003] In view of such problems of the prior art, a primary object ofthe present invention is to provide stationary vanes for turbines thatare efficient and can be manufactured both easily and economically.

[0004] A second object of the present invention is to provide stationaryvanes for turbines that can be made from roll formed or extrudedmaterial without requiring an extensive machining process or anelaborate casting process.

[0005] A third object of the present invention is to provide a methodfor making such stationary vanes.

[0006] According to the present invention, such objects can beaccomplished by providing a stator vane for a turbine, characterized bythat: the vane is provided with a leading edge which is cut into adifferent depth in dependence on a span-wise position so that a bladeinlet angle may vary along a span-wise direction according to aprescribed pattern.

[0007] By thus optimizing the depth of the cut along the leading edge ofthe stator vane, the leading edge blade inlet angle can be optimizedalong the entire length of the stator vane even if the stator vaneconsists of a two-dimensional aerofoil, and the vane is provided with asubstantially conformal cross section in parts which are not affected bythe cut in the leading edge. Thereby, the efficiency of the turbine canbe optimized.

[0008] Thus, the vane may be made of a roll formed plate member or anextruded plate member.

[0009] The stator vane defined above can be manufactured by preparing aplate member having a substantial same cross section substantially overan entire length thereof; and cutting a side edge of the plate member bya varying depth along an axial length thereof according to a prescribedpattern. The cut leading edge may be beveled, chamfered or otherwiserounded.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Now the present invention is described in the following withreference to the appended drawings, in which:

[0011]FIG. 1 is a perspective view of a conventional three-dimensionalstator vane;

[0012]FIG. 2 is a perspective view of a conventional two-dimensionalstator vane;

[0013]FIG. 3 is a schematic view of a stator vane array showing thedefinition of the leading edge blade inlet angle;

[0014]FIG. 4 is a perspective view of a two-dimensional stator vanehaving a leading edge cut into a different depth along the span-wisedirection thereof according to the present invention;

[0015]FIG. 5 is a graph showing the relationship between the cut depthand leading edge blade inlet angle β;

[0016]FIG. 6 is a graph showing a desired distribution of cut depthalong the span-wise direction of the vane; and

[0017]FIG. 7 is a graph showing the distributions of pressure loss alongthe span-wise direction of the vane for the three different kinds of thestator vanes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018]FIG. 1 shows a conventional three-dimensional stator vane 1 whichis slightly twisted around a span axis. In other words, the chorddirection varies depending on the position along the span direction.According to this structure, the distribution of the blade inlet angleof the leading edge 2 along the span direction can be selected at willso that the efficiency of the turbine can be optimized in a favorablemanner. However, because the cross sectional shape of the vane variesalong the span direction, a casting process or computer-controlledmachining process is required for the manufacture of the vane, and thiscauses a high manufacturing cost.

[0019]FIG. 2 shows a simple two-dimensional vane which is formed bybending a plate member. A certain minimum wall thickness is required tobe ensured for a casting process to be executed in a satisfactorymanner. On the other hand, if the vane is made of light weight platemember, the wall thickness can be determined at will, and a morelight-weight design is possible as compared to a comparable castthree-dimensional vane. In this case, because the cross sectional shapeis fixed along the span direction, the manufacturing process is bothsimple and economical, but a certain drop in the efficiency isinevitable because the blade inlet angle of the leading edge 2 is fixedalong the span direction.

[0020]FIG. 3 schematically illustrates an array of turbine stator vanes,and shows the definition of the leading edge blade inlet angle β. Theleading edge blade inlet angle β is given as the angle of the tangent ofthe center line of the leading edge with respect to the axial directionof the turbine. Typically, the leading edge blade inlet angle shouldalign with the direction of the incoming flow or the flow inlet angle,but the actual flow inlet angle varies depending on the radial positionof the turbine or the span-wise position of each vane.

[0021]FIG. 4 shows a two-dimensional stator vane according to thepresent invention. In this case also, the stator vane 1 is formed bybending a plate member. The cross section of the work piece is conformalalong the span direction thereof, but the stator vane is subjected to amachining process so as to have a chord length which varies depending onthe span-wise position. Thus, the vane is provided with a substantiallyconformal cross section in parts which are not affected by the cut inthe leading edge.

[0022] The machined part of the stator vane is appropriately beveled,chamfered or otherwise rounded so as to eliminate any cause ofaerodynamic losses. The base end structure for securing the stator vane1 such as a dovetail lock can be formed by welding a separate memberthereto. The stator vane 1 may also be formed from an extruded member.The cross section of the vane 1 may consist of either an aerofoilconfiguration for an optimum aerodynamic performance or a more simpleshape for an economic advantage.

[0023]FIG. 5 is a graph showing the change of the leading edge bladeinlet angle β in dependence on the depth of the machined cut x from thenominal leading edge of a vane having the chord length of D. Thenecessary cut depth for a desired value of the leading edge blade inletangle β can be obtained from this graph.

[0024]FIG. 6 is a graph that shows the distribution of the desired flowinlet angle or the blade inlet angle in dependence on the span-wiseposition y in a turbine using vanes having a span length of L. Bydetermining the cut depth from the nominal leading edge in dependence onthe span-wise position y according to the data represented in FIGS. 5and 6, an optimum vane design can be achieved.

[0025]FIG. 7 shows the distributions of pressure loss in dependence onthe span-wise direction for vanes having different cross sectionalshapes. When a simple two-dimensional vane is used, a substantialpressure loss is produced in a span-wise outer end of the vane. However,a two-dimensional vane provided with a cut in the leading edge accordingto the present invention can reduce the pressure loss to a substantiallysame level as that of a three-dimensional vane.

[0026] Thus, according to the present invention, an efficiencycomparable to that of a three-dimensional vane can be achieved while thecost and weight can be reduced to those of a two-dimensional vane.

[0027] Although the present invention has been described in terms of apreferred embodiment thereof, it is obvious to a person skilled in theart that various alterations and modifications are possible withoutdeparting from the scope of the present invention which is set forth inthe appended claims.

1. A stator vane for a gas turbine engine, characterized by that: saidvane is provided with a leading edge which is cut into a different depthin dependence on a span-wise position so that a blade inlet angle mayvary along a span-wise direction according to a prescribed pattern.
 2. Astator vane according to claim 1, wherein said vane is provided with asubstantially conformal cross section in parts which are not affected bysaid cut in said leading edge.
 3. A stator vane according to claim 1,wherein said vane is made of a roll formed plate member.
 4. A statorvane according to claim 1, wherein said vane is made of an extrudedplate member.
 5. A stator vane according to claim 1, wherein said cutleading edge is beveled, chamfered or otherwise rounded.
 6. A method ofmaking a stator vane for a gas turbine engine, comprising the steps of:preparing a plate member having a substantial same cross sectionsubstantially over an entire length thereof; and cutting a side edge ofsaid plate member by a varying depth along an axial length thereofaccording to a prescribed pattern.
 7. A method of making a stator vaneaccording to claim 6, wherein said vane is made of a roll formed platemember.
 8. A method of making a stator vane according to claim 6,wherein said vane is made of an extruded plate member.
 9. A method ofmaking a stator vane according to claim 6, wherein said cut leading edgeis beveled, chamfered or otherwise rounded.